mysql query 2 tables with count

Hi i have the following query/table from a local bookstore

$queryadmin ="SELECT last_name, first_name, user_id FROM users";
$recordz = @mysqli_query ($dbc, $queryadmin);

while ($row = mysqli_fetch_array($recordz, MYSQLI_ASSOC)) {
echo '<tr>
<td align="left">' . $row['first_name'] . '</td>
<td align="left">' . $row['last_name'] . '</td>
<td align="left">' . $row['user_id'] . '</td>
</tr>'
;} 

now i want an additional column from another table where the numbers of books each user has lend out are displayed. So the query if nested seperately would go something like this

$query2 = mysql_query("SELECT FROM mirror3 WHERE userid='".$row['user_id']."'", $link); 
$anzahl = mysql_num_rows($query2);  

开发者_如何学Goplacing this query nested inside the while query (right after while starting) from above does not work. How to do that?

supplied argument is not a valid MySQL result resource

thanks

Your query is wrong. Specify a field name:

$query2 = mysql_query("SELECT SOMETHING FROM mirror3 WHERE userid='".$row['user_id']."'", $link);

You could probably do this in one query:

$query = mysqli_query('SELECT u.last_name, u.first_name, u.user_id, m.PUT_SOMETHING_HERE
        FROM users u
        LEFT JOIN mirror3 m ON u.user_id = m.userid
        WHERE m.PUT_SOMETHING_HERE IS NOT NULL');

But Parkyprg has a point, you need to be selecting something from that second query.